1. Field
Apparatuses consistent with the exemplary embodiments relate to a backlight unit and a display apparatus including the same, and more particularly, to a backlight unit which provides necessary light by maintaining a gap between a light source unit and a light guiding plate regardless of expansion or contraction of the light guiding plate due to heat, and a display apparatus including the same.
2. Description of the Related Art
Backlight units may be classified as a direct type backlight unit and an edge type backlight unit depending on a location of a light source.
The direct type backlight unit has a light source disposed below a liquid crystal panel so that the light source emits light directly to the liquid crystal panel. The direct type backlight unit includes a reflection plate which is located under a lamp to reflect light, and an optical sheet which is disposed above the lamp to focus and diffuse the emitted light. As the direct type backlight unit may include a plurality of light sources and provide high efficiency in using light, it is mainly employed in a large-screen liquid crystal display (LCD) device that requires high brightness.
An edge type backlight unit typically has a light guiding plate disposed at a lateral side of a light source to guide light from a light source to a liquid crystal panel. The edge type backlight unit has a lower brightness when employed in a large-screen liquid crystal display device, but is advantageous in a thin display device. The light guiding plate diffuses light to make it uniform. Below the light guiding plate is provided a reflection plate. Above the light guiding plate, a pair of prism sheets which convert a path of light, and a diffusion sheet which reinforces uniformity of light incident to the liquid crystal panel are formed.
Generally, the light guiding plate includes polymer methyl methacrylate (PMMA). The PMMA expands and contracts in reaction to changes in temperature and moisture, and has a large expansion coefficient among other plastic materials.
In case of a large backlight unit, a light emitting diode (LED) employed as a light source should be as close to the light guiding plate as possible to provide sufficient light. The greater the gap between the LED and the light guiding plate is, the lower light efficiency is. If an LED is employed in an edge type backlight unit have a size greater than 40 inches, the size of the light guiding plate also increases. Thus, changes in the size of the light guiding plate (i.e., expanding or contracting) due to heat or moisture increases. If the LED is closely provided to the light guiding plate for light efficiency, the light guiding plate expands in a high-temperature operation environment and contacts the LED. On the contrary, if the gap between the LED and the light guiding plate increases to solve the foregoing issue, it is difficult to provide necessary light.